The present invention relates to a decorative film having a rainbow color appearance and a method for the production of the same.
Films having a rainbow color appearance are often used for decoration. Such decorative films have a multi-layer structure having a diffraction grating which presents a rainbow color appearance through light interference.
For example, JP-A-62-231753 discloses, as a laminate for decoration, a film comprising a substrate of a thermosetting resin and a reflective thin film formed on said substrate and made of a metal having thin striped uneven patterns which are formed in parallel with each other. In this laminate, the above uneven patterns, which are formed on the reflective thin film, function as a diffraction grating. In general, the reflection-type diffraction grating can provide a rainbow color appearance having a higher contrast than a transmission-type diffraction grating, when it is illuminated with light having a high intensity.
Furthermore, JP-A-62-231753 describes that the uneven patterns are in parallel with each other, and thus the film can provide a high luminance in a specific direction and give a high quality image to the rainbow color appearance.
The film of the above JP-A publication, which provides a high luminance in the specific direction, cannot present rainbow color appearance in many directions. That is, the rainbow color appearance greatly changes depending on observing direction. Such heterogeneity of the rainbow color appearances is less preferable from the viewpoint of visibility.
In the production process of such a film, a thermosetting resin layer is laminated on a substrate and incompletely cured, and a metal is vapor deposited on the thermosetting resin layer. Then, the thermosetting resin layer is completely cured and shrunk, whereby the deposited metal layer crinkles to form a reflective thin layer having uneven patterns.
However, the above curing reaction of a thermosetting resin is an irreversible reaction which is difficult to control. The difficulty of the control of this reaction further increases since this reaction is induced by heat which is in general difficult to manage. As the result, films having constant quality cannot be produced, and they cannot present the rainbow color appearances with good reproducibility. In addition, the curing reaction proceeds in two steps. Thus, the setting of the process conditions becomes difficult, and the process window is significantly narrowed. As the result, decorative films having intended rainbow color appearances may not easily be produced.
Accordingly, the objects of the present invention are to provide a decorative film which presents rainbow color appearances irrespective of observing directions, and to provide a method for easily producing such a film having constant quality.
The present invention has been completed to solve the above problems, and provides a decorative film comprising
the first resin layer comprising a light-transmitting first resin,
the second resin layer which is formed on at least a part of the surface of said first resin layer and comprises a light-transmitting second resin having a larger coefficient of thermal expansion than that of the first resin, and
a metal layer formed on said second resin layer, wherein the thickness of said second resin layer is from 0.3 to 0.8 xcexcm, and
said metal layer has uneven parts having a pitch width of 3.0 xcexcm or less which are randomly formed in contact with at least said second resin layer, and also a method for producing a decorative film comprising the steps of:
(A) forming a decorative film precursor by
providing the first resin layer comprising a light-transmitting first resin,
forming the second resin layer of a light-transmitting second resin having a thickness of from 0.3 to 0.8 xcexcm on at least a part of the surface of said first resin layer, said second resin having a larger coefficient of thermal expansion than that of the first resin, and
forming a metal layer on said second resin layer, and
(B) heating said decorative film precursor to randomly form uneven parts in the metal layer having a pitch width of 3.0 xcexcm or less in contact with at least said second resin layer.